In 2010, we reported a new method to electronically tailor the hole concentration of the high-Tc superconductor Bi2Sr2CaCu2O8+delta (Bi-2212). We discovered that current injection along the c-axis of Bi-2212 provides a convenient tool to reversibly increase the carrier concentration. In this study, we have investigated the current injection effect on the surface junction of Bi-2212 by a series of current injection experiments carried out in samples of slightly overdoped and of extremely underdoped Bi-2212 crystals. The c-axis transport characteristics of bulk and surface intrinsic Josephson junctions are examined in a wide range of doping by current injection. Before injection treatment, typically, our samples demonstrate non-superconducting characteristics across their surface junctions, because standard preparation procedures cause the topmost CuO2 layers to be heavily degraded by oxygen loss. The electronic doping enables to substantially restore the hole concentration of the topmost CuO2 layers. The contact resistance is significantly reduced, and the intrinsic junction at the surface gets back its superconducting tunneling characteristic. We examine systematically the doping results of surface and bulk junction stacks and discuss the enhancement of their superconducting properties.

The syntheses and structures of four new bis(pyrazol‐1‐yl)acetate‐ or bis(3,5‐dimethylpyrazol‐1‐yl)acetate‐based bis‐ligand nickel(II) complexes [Ni(bdmpzmp)2] (1), [Ni(bdmpzpen)2] (2), [Ni(bdmpza)2] (3), and [Ni(bpza)2] (4) are described. The results of single crystal structure determinations reveal for all four complexes κ3‐coordination of the scorpionate ligands. The sterically hindered bis(3,5‐di‐tert‐butyl‐pyrazol‐1‐yl)acetateto (bdtbpza) ligand allows the synthesis of the nickel(II) chlorido complex [Ni(bdtbpza)Cl] (5). Furthermore, controlled formation of a novel trinuclear linear complex [Ni(bdmpza)2{Ni(acac)(bdmpza)}2] (6) [bdmpza = bis(3,5‐dimethylpyrazol‐1‐yl)acetate] by a self‐assembling reaction and alkali metal‐mediated template syntheses of [Na{Ni(acac)(bdmpza)}3]NO3 (7), [Na{Ni(acac)(bdmpza)}3]I (8) and [Li{Ni(acac)(bdmpza)}3]NO3 (9) are reported. ESI MS allowed a detailed characterization in solution and is supported by X‐ray structure analysis. Compounds 7, 8 and 9 exhibit [12‐MC‐3] metallacrown structures with a sixfold coordinated alkali metal ion in the center. The magnetic properties are studied by SQUID. Crystallographic data reveal broken symmetry in the solid state for all three [12‐MC‐3] metallacoronates 7, 8 and 9. The linear structure of [Ni(bdmpza)2{Ni(acac)(bdmpza)}2] (6) (length ≈ 2 nm) obtained through synthesis without template, as well as the molecular structure of the [12‐MC‐3] metallacoronates 7, 8 and 9 (∅ ≈ 1.3 nm) are at the nanoscale.

The generic structure of most high Tc superconductors is a stacking sequence of superconducting planes separated by so‐called charge reservoir layers. It is well known that carrier doping of these materials is achieved either by substitution of atoms or by nonstoichiometry in the charge reservoir layer. The alternating type of stacking causes yet another two important consequences. First, the transport anisotropy of these materials can be so high, that in the superconducting state the c‐axis transport is governed by the intrinsic Josephson effect. Whereas the anisotropy of our investigated LaO1–xFxFeAs samples was not sufficient, optimum‐doped Ca10(FeAs)10Pt4As8 showed hysteretic c‐axis current–voltage characteristics. Together with the Ambegaokar–Baratoff like temperature dependence of the critical current, this is a strong indication of intrinsic Josephson effects. Second, it is possible to deposit in the charge reservoir layers a substantial amount of charge only by injecting large c‐axis currents. By charge compensation, this decreases the concentration of mobile electrons in the conducting layers of electron‐doped materials. We were able to verify this in all details by c‐axis transport measurements of LaO1−xFxFeAs single crystals and pure and Pt doped (CaFe1–xPtxAs)10Pt4As8 single crystals. After current injection, we observed a decrease of Tc for doping levels at or below the Tc maximum, and a Tc increase for doping levels beyond the maximum. In all cases, the resistivity of the samples increased significantly. In both material classes, heavily overdoped samples showed a spectacular Tc increase by more than 10 K only accomplished by carrier injection.Generic stacking sequence of layered superconductors and crystal structure of the pnictide LaOFeAs.

Starting from nickel(II) cubane [Ni-4(II)(HL)(4)(OAc)(4)] (2a), five different tetranuclear cubic complexes [Ni-4(II)(HL)(4)(O2CR)(4)] (3) were generated simply by applying a post-synthetic cubane modification strategy via a complete acetate-to-carboxylate co-ligand exchange. This was achieved by stirring the parent complex 2a with a large excess of the corresponding sodium carboxylate salt 4 for three days in THF. Single-crystal X-ray structure analyses of Ni-II cubanes 3a2Et(2)O and 3b0.5CH(2)Cl(2)0.5Et(2)O reveal unequivocally that both are isostructural in terms of the [Ni-4((3)-O-4](4+) core and crystallize in the triclinic space group P-1 with two molecules in the unit cell. In the solid state, the cubic centers of 3a,b differ only slightly in bond lengths and angles mainly due to the different substituents in the carboxylate co-ligand and packing in the unit cell. The orientation of 3a,b and the formation of supramolecular aggregates in the crystal packing were controlled by - interactions as well as intra- and intermolecular O-HO hydrogen bonds. Variable-temperature magnetic susceptibility measurements reveal that 3a-c show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for all investigated complexes. [GRAPHICS] .

•The triplesalen ligand has been rationally designed for a targeted synthesis of SMMs.•Heptanuclear [MnIII6CrIII]3+ and [MnIII6MnIII]3+ triplesalen complexes are indeed SMMs.•High molecular and crystal symmetry reduces zero-field tunneling.•This is due to vanishing transversal components (dipolar and rhombic terms).•Five requirements are formulated for increasing the blocking temperatures of SMMs.

Our recently discovered electrical doping technique allows a broad-range variation of carrier concentration without changing the chemical composition. We show that it is possible to induce superconductivity in a nondoped insulating sample and to tune it reversibly all the way to an overdoped metallic state. This way, we can investigate the whole doping diagram of one and the same sample. Our study reveals two distinct critical points. The one at the overdoped side is associated with the onset of the pseudogap and with the metal-to-insulator transition in the $c$-axis transport. The other at optimal doping is associated with the appearance of a ``dressed'' electron energy. Our study confirms the existence of multiple phase transitions under the superconducting dome in cuprates.

Under anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6-pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) complexes [M-4(II)(HL2)(4)(OAc)(4)] (4; M-II = Co2+, Ni2+) with a [M-4(mu(3)-O)(4)](4+) cubane core. X-ray structural analyses revealed that both MII cubanes 4a center dot 2CH(3)OH and 4b center dot 2CH(3)OH are isostructural and crystallize in the tetragonal space group I4(1)/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by pi-pi interactions as well as intra- and intermolecular O-H center dot center dot center dot O hydrogen bonds. Variable-temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core-level X-ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X-ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge-transfer multiplet simulations.

Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuCl{N(CH2 CH2 PtBu2 )2 }], [RuCl{N(CHCHPtBu2 )(CH2 CH2 PtBu2 )}], and [RuCl{N(CHCHPtBu2 )2 }], in which the ruthenium(II) ions are in the extremely rare square-planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet (S=0) ground state and energetically low-lying triplet (S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet (S=1) ground states as confirmed by experimental and computational examination. However, essentially non-magnetic ground states arise for the two intermediate-spin complexes owing to unusually large zero-field splitting (D>+200 cm(-1) ). The change in ground state electronic configuration is attributed to tailored pincer ligand-to-metal π-donation within the PNP ligand series.

Superparamagnetic iron oxide nanoparticles (SPIONs) with a mixed phase composition (gamma-Fe2O3)(1-x)(Fe3O4)(x) and sizes between 9 and 20 nm were synthesized via coprecipitation and were either left uncoated or subsequently surface-stabilized with citrate or malate anions. The sizes, morphology, surface chemistry, and magnetic properties of the nanoparticles were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and superconducting quantum interference device measurements, respectively. Cellular uptake and intracellular distribution in normal tissue and tumor cells were verified by TEM images. X-ray-induced changes of the oxidation state and site geometries of surface iron ions of uncoated and citrate-coated SPIONs were explored by collecting Fe K-edge X-ray absorption spectroscopy data. The potential applicability of citrate- and malate-coated SPIONs as an X-ray enhancer for radiation cancer therapy was substantiated by their drastic enhancement of the concentration of reactive oxygen species (ROS) in X-ray irradiated tumor cells.

In this work, the authors focus on a method to fabricate arbitrary shaped free standing membranes with a thickness less than 20 nm, produced from different polymers with the help of low-energy ion irradiation. The authors analyze the thickness of the membranes and its dependence on the details of the irradiation process. In order to tune the properties of the suspended membranes, an additional ion irradiation step has been used. This step is applied to already suspended membranes and leads to several effects, such as heating, shape transformation, etc. These effects were analyzed for irradiation with Ar+ and He+ ions. The authors have found that He+ irradiation has a significant advantage over Ar+ irradiation providing strained, smooth, and homogeneous membranes. In order to measure the electrical properties of the suspended membranes, the authors invented a new method to contact the membranes. These low resistance contacts can be achieved as the authors describe in detail. The membranes electrical properties after He+ ion irradiation at different temperatures are presented. Finally, the authors analyze Raman spectra, and thermal and electrical conductivity of the highly conducting membranes. The authors conclude that after high temperature He+ ion irradiation the membranes consist of material similar in properties to the glassy carbon obtained by pyrolysis. However, this method does not require high temperature pyrolysis step, which makes integration with on-chip electronics more feasible.

A decanuclear cobalt(II) phosphonate, [Co10{2,3,5,6-(Me)4C6HCH2PO3}8{2,3,5,6-(Me)4C6HCH2PO3H}4Cl6]·6Et3NH·10n-hexane·16H2O (1) with a planar arrangement of the CoII ions is described. This compound shows slow relaxation of its dynamic magnetization.

Novel κ(3) -N,N,O ligands tend to form 1D coordination polymer strands. Deposition of 1D structures on highly oriented pyrolytic graphite (HOPG) was achieved from diluted solutions and polymer strands have been studied on HOPG by AFM/STM. Single strands were mapped by STM and their electronic properties were subsequently characterized by current imaging tunneling spectroscopy (CITS). Periodic density functional calculations simulating a polymer strand deposited on a HOPG surface are in agreement with the zig-zag structure indicated by experimental findings. Both the observed periodicity and the Zn-Zn distances can be reproduced in the simulations. Van der Waals interactions were found to play a major role for the geometry of the isolated polymer strand, for the adsorption geometry on HOPG, as well as for the adsorption energy.

Graphene oxide can be used as a precursor to graphene, but the quality of graphene flakes is highly heterogeneous. Scanning Raman microscopy (SRM) is used to characterize films of graphene derived from flakes of graphene oxide with an almost intact carbon framework (ai-GO). The defect density of these flakes is visualized in detail by analyzing the intensity and full width at half-maximum of the most pronounced Raman peaks. In addition, we superimpose the SRM results with AFM images and correlate the spectroscopic results with the morphology. Furthermore, we use the SRM technique to display the amount of defects in a film of graphene. Thus, an area of 250 X 250 mu m(2) of graphene is probed with a step-size increment of 1 mu m. We are able to visualize the position of graphene flakes, edges and the substrate. Finally, we alter parameters of measurement to analyze the quality of graphene in a fast and reliable way. The described method can be used to probe and visualize the quality of graphene films.

TT 26.1 Tue 9:30 H17 Transport properties of high-quality reduced graphene oxide — ∙Michael Enzelberger1, Siegfried Eigler2, Philipp Hofmann1, Stefan Grimm2, Andreas Hirsch2, and Paul Müller1 — 1Department of Physics and Interdisciplinary Center for Molecular Materials, Universität Erlangen-Nürnberg — 2Department of Chemistry and Pharmacy, and Institute of Advanced Materials and Processes (ZMP), Universität Erlangen-Nürnberg

The reaction between Ln(III) chloride and NiCl2·4H2O salts in presence of a multidentate sterically unencumbered ligand, (E)-2,2'-(2-hydroxy-3-((2-hydroxyphenylimino)methyl)-5-methylbenzylazanediyl)diethanol (LH4) leads to the synthesis of four isostructural pentanuclear hetereometallic complexes [Ni2Dy3(LH)4]Cl (1), [Ni2Gd3(LH)4]Cl (2), [Ni2Tb3(LH)3(LH2)]Cl2 (3), [Ni2 Ho3 (LH)3 (LH2)]Cl2 (4) with unprecedented topology. Here the two compounds 1 are 2 are monocationic and crystallize in chiral space group, P2(1)2(1)2(1) whereas compounds 3 and 4 are dicationic and crystallize in achiral space group P2(1)/n. The total metal framework, {Ni2Ln3} unit is held by four triply deprotonated ligands [LH](3-) in 1 and 2 whereas in case of 3 and 4 three triply deprotonated [LH](3-) and one doubly deprotonated [LH2](2-) ligands are involved. In these complexes both the lanthanide ions and the nickel(II) ions are doubly bridged and the bridging is composed of oxygen atoms derived from either phenolate or ethoxide groups. The analysis of SQUID measurements reveal a high magnetic ground state and a slow relaxation of the magnetization with two relaxation regimes for 1. For the thermally activated regime we found an effective energy barrier of U(eff) = 85 K. Micro Hall probe loop measurements directly proof the single-molecule magnet (SMM) nature of 1 with a blocking temperature of T(B) = 3 K and an open hysteresis for sweep rates faster than 50 mT/s.